Aluminum-steel composites

ABSTRACT

COMPOSITES OF ALUMINUM AND STEEL ARE DISCLOSED WHICH ARE RESISTANT TO INTERMETALLIC FORMATION. THE COMPOSITES ARE CHARACTERIZED BY THE ALUMINUM COMPONENT CONTAINING FROM 0.5 TO 2.5% SILICON AND THE STEEL COMPONENT CONTAINING FREE OR SOLUBLE NITROGEN IN AN AMOUNT FROM 0.001 TO 0.05%. THE COMPOSITE RESULTS IN A SYNERGISTIC SYSTEM EXHIBITING REMARKABLE RESISTANCE TO INTERMETALLIC FORMATION WHEN THE COMPOSITE IS ANNEALED.

United States Patent O 3,705,023 ALUMINUM-STEEL COMPOSITES Julius C.Fister, Jr., Hamdeu, Conn., assignor to Olin Corporation No Drawing.Filed Dec. 18, 1970, Ser. No. 99,672 Int. Cl. B23p 3/00 US. Cl. 29196.25 Claims ABSTRACT OF THE DISCLOSURE Composites of aluminum and steel aredisclosed which are resistant to intermetallic formation. The compositesare characterized by the aluminum component containing from 0.5 to 2.5%silicon and the steel component containing free or soluble nitrogen inan amount from 0.001 to 0.05%. The composite results in a synergisticsystem exhibiting remarkable resistance to intermetallic formation whenthe composite is annealed.

BACKGROUND OF THE INVENTION Composites of aluminum and steel findextensive use in industry. For example, they are useful in theelectronics industry, in underground cable sheathing, and in areas wherethe aluminum component provides oxidation and corrosion protection forthe steel component.

A great many of the areas of use for this type of composite require anannealing operation in order to soften the composite for forming. Duringthe annealing operation, there is a strong tendency for interdifiusionto occur between the aluminum component and the steel component and forma brittle intermetallic compound. The brittle intermetallic compoundwhich forms significantly reduces the bond strength and, hence,significantly limits the usefulness of the resultant composite.

It would naturally be highly desirable to substantially eliminate thisbrittle layer. The elimination of the brittle intermetallic compoundwould greatly extend the usefulness of aluminum-steel composites andwould extend the number of products which could be made therefrom.Elimination of the brittle layer would greatly minimize the cost andcare currently required to keep the intermetallic layer at acceptablelevels.

Art processes have been suggested to minimize intermetallic formation.For example, US. Pat. 2,965,963 contemplates the use of soluble oractive nitrogen in order to reduce intermetallic formation. However,this patent does not completely eliminate intermetallic formation. Also,this teaching often causes processing difiiculties. In order to softenthe steel component, the procedure requires annealing at temperaturesthat tend to form some intermetallics.

In general, art processes do not completely eliminate intermetallicformation and often limit the annealing time and temperature. Thisfrequently results in a product with reduced intermetallic formation buta product that is not softened completely thereby causing subsequentprocessing problems.

Accordingly, it is a principal object of the present invention toprovide novel aluminum-steel composites.

It is an additional and principal object of the present invention toprovide aluminum-steel composites which eliminate the problem ofintermetallic compound formation between the aluminum and steelcomponents.

Further objects and advantages of the present invention will appear fromthe ensuing discussion.

SUMMARY OF THE INVENTION In accordance with the present invention it hasnow been found that the foregoing objects and advantages may ice bereadily achieved and a composite provided which overcomes artdisadvantages.

The composite of the present invention consists essentially of analuminum component and a steel component. The aluminum componentcontains silicon in an amount from 0.5 to 2.5%. The steel componentcontains free or soluble nitrogen in an amount from 0.001 to 0.050% andalso has a carbon content of from 0.01 to 1%.

The composites of the present invention readily overcome thedisadvantages of the art and have been found to exhibit remarkableresistance to intermetallic compound formation when annealed. It isbelieved that a synergistic system exists when the silicon is added tothe aluminum component and the free or soluble nitrogen is added to thesteel component which system virtually eliminates intermetallic compoundformation.

The composites of the present invention overcome previous processingdifliculties. Due to the lack of intermetallic formation, the materialcan be softened at elevated temperature and allows attainment of optimumproperties in the composite, especially in the steel component andespecially good ductility.

DETAILED DESCRIPTION As indicated hereinabove, any aluminum alloy may beemployed which contains the requisite quantity of silicon, namely from0.5 to 2.5% and preferably from 1 to 2%. Thus, for example, the aluminumalloy may contain other alloying additions as desired or conventionalimpurities. Representative alloying additions which may be readilyemployed are the following materials in the following amounts: boron, upto 1%; copper, up to 3%; zinc, up to 4%; magnesium, up to 5%; iron, upto 3%; and manganese, up to 2%.

The steel component should contain carbon in an amount from 0.01 to 1%.Preferably, the steel component is a low carbon steel containing 0.15%carbon max. Other materials which are readily contemplated in the steelcomponent are, for example, aluminum, vanadium, boron, titanium andniobium. Elements which are preferential nitride formers should beavoided.

As indicated hereinabove, the composite of the present inventionrequires that the steel component contain free or soluble nitrogen in anamount from 0.001 to 0.050%. By free or soluble nitrogen it is meantthat nitrogen be present in the steel component in theamounts listed indissolved or uncombined form. That is, if the nitrogen is in the form ofnitrides or other nitrogen containing compounds, these stable nitridesare not considered free or soluble nitrogen.

The composite may be prepared in any desired manner. A particularlypreferred method of preparing the composite involves rolling thecomponents together in direct face-to-face contact in order to form anintegral firmly bonded composite as disclosed in, for example, U .S.Pats. 3,462,827 and 3,462,828. Any desired method of forming thecomposite may, however, be readily employed.

The present invention will be more readily apparent from a considerationof the following illustrative examples.

Example I A composite was prepared wherein the aluminum component was analuminum base alloy containing: 1.25% silicon; 0.35% iron; 0.012%magnesium; 0.004% copper; and 0.007% manganese. The steel component wasa 1010 low carbon steel containing 0.1% carbon, 0.5% manganese, 0.04%phosphorus and 0.05% sulfur and which contained free or soluble nitrogenin an amount of about 0.003%.

Prior to bonding, the aluminum component had a thickness of 0.010" andthe steel component had a thickness of 0.042". The aluminum componentwas annealed at 650 F. for 1 hour prior to bonding and the steelcomponent was used in the as-received or annealed condition. Thecomponents were degreased, washed, rinsed, dried and wire brushed priorto bonding. A 2" wide x 10 long strip of the aluminum component wasfolded over the appropriate 2" wide x 5" long strip of the steelcomponent and the resultant assembly was given a 55 to 60% single passcold reduction which resulted in a firmly bonded composite. Theresultant composite was then rolled to the desired gage of 0.010".

Samples of the resultant composite were annealed at 1050 F. for 1 hour.Additional samples were annealed at 1050 F. for 16 hours. The resultantsamples were metallographically examined at a magnification of 1000 forevidence of an intermetallic layer at the interface. The result was thatno intermetallic layer could be observed on either sample due to thecombined or synergistic effect of the silicon in the aluminum componentand the free or soluble nitrogen in the steel component.

Example II Example I was repeated except that the aluminum component wasa high purity aluminum (99.99% The steel component was the same as inExample 1. The composite was prepared in the same manner as Example Iand the resultant material was given a 1 hour anneal at 1050 F. Themetallographic examination of the resultant material showed a 2 tomicron thick intermetallic layer at the interface.

Example III Example -I was repeated with the exception that the steelcomponent was an aluminum killed 1010 steel which contained 0.0047%nitrogen which existed as aluminum nitride particles. The composite wasprepared in the same manner as Example I and the resultant composite wasannealed for 1 hour at 1050 F. Metallographic examination showed anintermetallic layer in excess of 20 microns between the aluminum andsteel components and the components split apart due to the thickness andbrittle material of the intermetallic layer.

Example IV Example I was repeated with an aluminum alloy containing:magnesium, 0.9%; silicon, 0.65%; iron, 0.2%;

4 copper, 0.03%; zinc, 1.00%; boron, 0.022% and manganese, 0.03%. Onceagain, no intermetallic layer could be observed in the resultantproduct.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit.

or essential characteristics thereof. The present embodiment istherefore to be considered as in all respects illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims, and all changes which come within the meaning and range ofequivalency are intended to be embraced therein.

What is claimed is:

1. An aluminum-steel composite free from intermetallic compoundformation wherein the aluminum component is an aluminum base alloycontaining silicon in an amount from 0.5 to 2.5% and wherein the steelcomponent contains free nitrogen in an amount from 0.001 to 0.050% andhas a carbon content of from 0.01 to 1%.

2. A composite according to claim 1 wherein said aluminum componentcontains silicon in an amount from 1 to 2%.

3. A composite according to claim 1 wherein the steel component is a lowcarbon steel containing 0.15% max. carbon.

4. A composite according to claim 1 in the annealed condition.

5. A composite according to claim 1 wherein the a1uminum componentcontains boron up to 1.0%, copper up to 3.0%, zinc up to 4.0%, magnesiumup to 5.0%, iron up to 3.0% and manganese up to 2.0%.

References Cited UNITED STATES PATENTS 3,567,409 3/ 1971 Seiler 29196.23,579,313 5/1971 Pryor et al. 29196.2 3,607,151 9/1971 Pryor et a129-1962 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, AssistantExaminer US. Cl. X.R. -123 B, 143

